Eukaryotic transcriptional activators work by recruiting to DNA the transcriptional machinery, including protein complexes required for chromatin modification, transcription initiation, and elongation. Which of these complexes must be directly recruited to trigger transcription? We test various "non-classical" transcription activators (comprising a component of the transcriptional machinery fused to a DNA binding domain) for their abilities to activate transcription of a chromosomally integrated reporter in yeast. Among these newly constructed fusion proteins, none efficiently activated transcription when working on its own. However, in several instances transcription was activated by a pair of such fusion proteins tethered to adjacent sites on DNA. In each of these cases, one fusion protein bore a component of the SAGA complex, and the other bore a component of the Mediator complex. Transcription was also activated by certain tripartite fusion proteins comprising a Mediator and a SAGA component fused to a DNA binding domain. The results are consistent with the finding that the classical activator Gal4, working at the GAL1 promoter, activates transcription by (at least in part) independently recruiting SAGA and Mediator.

• PMID: 15380071
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Comparative Study | Journal Article | Research Support, U.S. Gov't, P.H.S.

Authors

Cheng JX, Gandolfi M, Ptashne M

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